One method of calculating to find a dermal reaction, prior to the present invention, included the illumination of a zone to be characterized on the skin via an excitation light beam emitted by a source of light, the skin reaction being included in the zone to be characterized, the measurement, by means of a spectrometer, of the spectrum of a back scattered radiation coming from the skin as a result of the illumination of said zone to be characterized, the determination, on the basis of the measured spectrum and for at least one given value of the wave length of the light beam, of a value of the absorption coefficient for the zone to be characterized, the calculation, on the basis of the or each determined value of the absorption coefficient, of the concentration of at least one chromophore in the skin, and the calculation, of the quantification indicator for quantifying the dermal reaction on the basis of the previously calculated concentration of the or each chromophore.
The present invention also relates to a system for calculating such a quantification indicator.
The invention is applicable in particular to the calculation of an indicator for the quantification of a patient's skin reaction following the intradermal injection of an active ingredient for the implementation of a test for the presence of antibodies in the organism, the test being for example the test for tuberculosis after an injection of tuberculin. The quantification indicator is thus a function of the immune response.
The invention is also applicable to the calculation of an indicator for the quantification of the skin reaction following the injection of an active ingredient capable of causing an allergic skin reaction.
The invention is more generally applicable to the calculation of an indicator for the quantification of any dermal reaction, such as an inflammation reaction, an induration reaction, or even a reaction involving alteration of the skin.
The article “Interpreting diffuse reflectance for in vivo skin reactions in terms of chromophores” by Kollias et al, published in the journal entitled Journal of Biophotonics, in 2010, describes a method and a system for calculation of the aforementioned type. This article is a quantitative interpretation of skin reactions based on the measurements of reflectance of the skin, in particular forming the assumption that the attenuation of the light during its propagation through the skin, obeys the Beer-Lambert law.
The method of operation is as follows. The skin is illuminated with a light beam emitted from a source of white light, the measurements of reflectance of a back scattered radiation due to the illumination of the skin are then performed with the aid of a spectrometer. The concentrations of chromophores in the skin, in particular the concentrations of melanin, oxyhaemoglobin and deoxyhaemoglobin, are calculated from the measured reflectance values.
The absorbance of the skin is considered to be dependent upon chromophore concentrations calculated on the basis of the values of reflectance measured. In the case of the formation of pigments induced by a simulated solar radiation, the only chromophore concentration taken into consideration for the quantification is the concentration of melanin. In the case of an inflammation induced by histamine, the chromophore concentrations taken into account are the concentrations of oxyhaemoglobin (HbO2) and water. The effect of the diffusion is approximated by taking into consideration an additional chromophore. Thus, diffusion is considered comparable to absorption linked to the concentration of this new chromophore.
Finally, in this paper, the authors have established the evolution of these chromophores based on certain inflammations. However, they do not calculate an index to enable quantifying the reaction of the skin based on these concentrations. By the authors' own admission, the relationships between the concentrations of different chromophores have not been explored in an exhaustive manner and thus remain to be established.
For their part, the inventors have found that it was necessary to establish a multi parameter indicator, that is to say, one that takes into account the concentration of various chromophores thereby enabling the quantifying of the skin reaction following injection of the active ingredient. Moreover, they observed that such quantification carried out by using different concentrations of chromophores is not always very precise, and a certain number of results are incorrect, with the reaction for example being incorrectly indicated as positive (false positive), or on the contrary being indicated as negative whereas it is positive in actual fact (false negative).